Irregular ferroelectric element devised for motion of plural domain-walls

ABSTRACT

An element in which only a single domain-wall can move sidewise, having a crystal plate of an irregular ferroelectric which is cut in the Z-plane at opposite surfaces and is then cut or cleaved in the &lt;110&gt; direction at its periphery and transparent electrodes for the polarization reversal provided at the central portions of the opposite Z-planes. The element includes at least a domain configuration such that two nucleus regions of opposite polarities are disposed on opposite sides of the region, i.e., a domain having a stationary polarity, where the electrodes are provided.

This is a division of application Ser. No. 16,199 filed Mar. 3, 1970,now U.S. Pat. No. 3,936,146.

This invention relates to an irregular ferroelectric single-domaincontrollable element which is devised for single domain-wall motion andto a method of making such an element. This invention also relates to anapparatus which utilizes such an irregular ferroelectric element.

It is a primary object of the present invention to provide an irregularferroelectric element for controllable single-domain in which only asingle domain-wall can move sidewise and which is free from the growthof nucleus regions crossing at right angles with respect to each otherand a method of making such an irregular ferroelectric element.

Another object of the present invention is to provide an irregularferroelectric element for controllable single-domain of the kinddescribed above in which the positive and negative domains can be freelygrown and extinguished.

A further object of the present invention is to provide an electricallycontrolled shutter for transmitted light which utilizes an irregularferroelectric element of the kind described above.

A still further object of the present invention is to provide an opticalslit which utilizes an irregular ferroelectric element of the kinddescribed above.

Another object of the present invention is to provide a two-dimensionalflying spot scanner which utilizes an irregular ferroelectric element ofthe kind described above.

In accordance with the present invention which attains the aboveobjects, there is provided a method of making an irregular ferroelectricelement for controllable single-domain which is devised for singledomain-wall motion comprising the steps of growing a single domain ofpositive or negative polarity throughout a Z-plate of irregularferroelectric relative to the opposite Z-planes of said crystal plate,provided with electrodes leaving from the abovementioned nucleus regionwhich has the same polarity as to the applied voltage and adjacent toone end of the domain of the inverse polarity against to the appliedvoltage grown in the first step in the same polarity as to the appliedvoltage and growing throughout a domain of the inverse polarity andarriving to the second nucleus region of the inverse polarity to thefirst nucleus region adjacent to the end opposite to the end having saidfirst nucleus region referred to in the second step and providing meansfor the polarization reversal and single domain-wall motion towards thenucleus region of inverse polarity.

In accordance with the present invention, there is further provided anirregular ferroelectric element for controllable single-domain devisedfor single domain-wall motion comprising a crystal plate of irregularferroelectrics which is provided with electrodes on Z-planes at a pairof surfaces opposite to each other and is then cut or cleaved in the<110> direction, and means for the polarization reversal provided at thecentral portions of the opposite Z-planes of said crystal plate, saidirregular ferroelectric element including at least a domainconfiguration such that two nucleus regions of opposite polarities aredisposed on opposite sides of the region where said means for thepolarization reversal are provided.

The present invention further provides an optical apparatus whichincludes therein such an irregular ferroelectric element such that theamount of light transmitted through the apparatus can be freelycontrolled by allowing the growth or restricting the growth of one ofthe nucleus domains of the irregular ferroelectric element.

The irregular ferroelectric element for controllable single domainaccording to the present invention has the following advantages:

1. The element is advantageous over a prior art element of this kindwhich resorts to a method of merely growing a new single domain inferroelectric crystal, because the element is free from any damage andthe motion of the domain-wall takes place readily in response to theapplication of a small voltage.

2. Switch-over of the applied voltage causes immediately the growth ofthe domain of opposite polarity from a domain having a stationarypolarity and the domain grown prior to the voltage switch-over can bereversed. Thus, the domain of positive or negative polarity can befreely grown as desired. In addition, the direction of the domain-wallmotion can be freely controlled by selecting the polarity of the appliedvoltage.

3. The rate of growth of the domain can be freely controlled byregulating the magnitude of the applied voltage.

4. The element can be combined with the other optical apparatus forapplication to various services.

Other objects, features and advantages of the present invention will bereadily apparent from the following detailed description taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a schematic explanatory view showing the manner of crystaldeformation occurring in a ferroelectric crystal due to the polarizationreversal;

FIG. 2 is a schematic explanatory view showing the mechanism of rotationof linearly polarized light by a ferroelectric crystal;

FIG. 3 is a diagrammatic view showing a portion of the refractiveindicatrix of a bi-axial crystal;

FIG. 4 is a schematic explanatory view showing how a change in theretardation of transmitted light occurs when linearly polarized light isprojected to an apparatus including the combination of an irregularferroelectric crystal and a common double refractive material;

FIGS. 5, 5a, 5b, 5c and 5d are schematic views showing the latticedeformation caused in an irregular ferroelectric crystal through thephase transition temperature from paraelectric phase into theferroelectric phase;

FIGS. 6a, 6b and 6c are schematic views showing a plurality of kinds ofdomain patterns produced in an irregular ferroelectric crystal;

FIG. 7 is a schematic view showing how domains crossing at right angleswith each other appear in a gadolinium molybdate (MOG) crystal;

FIGS. 8, 8a, 8b, 8c, 8d and 8e are schematic views showing thesuccessive steps for the manufacture of an irregular ferroelectricelement according to an embodiment of the method of the presentinvention utilizing the domain switching in an irregular ferroelectriccrystal;

FIGS. 9a and 9b are schematic views showing the successive steps inanother embodiment of the method of the present invention utilizing thedomain switching in an irregular ferroelectric crystal;

FIGS. 10a, 10b and 10c are schematic views showing the successive stepsin a further embodiment of the method of the present invention utilizingthe domain switching in an irregular ferroelectric crystal;

FIG. 11 is a schematic view showing a yet further embodiment of themethod of the present invention utilizing the domain switching in anirregular ferroelectric crystal;

FIGS. 12a, 12b and 12c show the structure of an electrically controlledshutter for transmitted light employing an irregular ferroelectricelement according to the present invention;

FIG. 13 shows the structure of an optical slit unit employing anirregular ferroelectric element according to the present invention;

FIG. 14 shows the structure of an electrically controlled shutter fortransmitted light employing two optical slit units of the kind shown inFIG. 13;

FIG. 15 shows the structure of another form of the electricallycontrolled shutter for transmitted light employing two irregularferroelectric elements according to the present invention;

FIG. 15a is a graph showing the time function of voltage applied to theirregular ferroelectric elements in the shutter shown in FIG. 15;

FIG. 16 shows the structure of an optical pulse generator employing theshutter shown in FIG. 15;

FIG. 17 shows the structure of a two-dimensional flying spot scanneremploying a plurality of groups of irregular ferroelectric elementsaccording to the present invention;

FIG. 18 is an explanatory view illustrating the structure and operatingprinciple of another two-dimensional flying spot scanner employing aplurality of irregular ferro-electric elements according to the presentinvention;

FIG. 19 shows the structure of an image generator employing thetwo-dimensional flying spot scanner shown in FIG. 18;

FIG. 20 shows the structure of another image generator employing thetwo-dimensional flying spot scanner shown in FIG. 18;

FIG. 20a shows the structure of still another image generator employingthe two-dimensional flying spot scanner shown in FIG. 18;

FIG. 21 shows the structure of yet another image generator employingtwo-dimensional flying spot scanner shown in FIG. 18;

FIGS. 22a and 22b are a front elevational view and a sectional view,respectively, of one form of the irregular ferroelectric elementaccording to the present invention;

FIG. 23 shows the structure of a slide projector employing the irregularferroelectric element shown in FIGS. 22a and 22b;

FIG. 24 shows the structure of another slide projector employing theirregular ferroelectric element shown in FIGS. 22a and 22b;

FIG. 24a shows an exemplary picture depicted on a half-wave plateassembly shown in FIG. 24, and

FIG. 25 shows the orthogonal domains produced in the irregularferroelectric element according to the present invention.

In U.S. Pat. No. 3,586,415, an optical modulator element comprising thecombination of an irregular ferroelectric crystal, especially anelectroded Z-plate of gadolinium molybdate single crystal provided withelectrodes and a double refractive crystal plate is disclosed. Accordingto the discovery of the inventors, application of an electric fieldwhich is at least equal to the coersive field of the said irregularferroelectric single crystal across the Z-planes of the irregularferroelectric single crystal can cause a change in the retardation oflight transmitting through the element before and after the applicationof the electric field, and thus this element can constitute a sort ofcolor-modulator for incident white light or a light intensity-modulatorfor incident monochromatic light.

As a result of profound investigation on the symmetry of ferroelectrics,the inventors have found that certain ferroelectric crystals such as acrystal of potassium dihydrogen phosphate (hereinafter to be referred toas KDP) and a crystal of gadolinium molybdate (hereinafter to bereferred to as MOG) behave differently from known ferroelectric crystalssuch as a crystal of triglycine sulfate (hereinafter to be referred toas TGS), a crystal of lead zirconate-titanate (hereinafter to bereferred to as LZT) and a crystal of barium titanate when an electricfield or stress of more than a threshold value (hereinafter to bereferred to as a coersive field or coersive stress) is applied thereto.More precisely, when a coersive field or coersive stress is applied to acrystal of KDP or MOG, the crystal lattice having bi-stable states asshown in FIG. 1a or 1b makes a shift from one spontaneously deformedstate to another and, simultaneously, a 180° reversal of the directionof the spontaneous polarization takes place. Further, simultaneouslywith the reversal in the direction of the spontaneous polarization, thecrystal lattice undergoes crystallographically a symmetry operation ofinversion rotation so that it is deformed into a structure which isrotated through 90° about the c axis. Such a property is peculiar tocertain ferroelectric belonging to the point group mm2. Suchferroelectrics were called by the inventors by the name of irregularferroelectrics and classified to belong to a point group imm2 includingsuch species as 42 mF mm2, 6 m2F mm2 and 43 mF mm2. A crystal of such anirregular ferroelectric is optically bi-axial in the ferroelectric phaseand the refractive indices α, β and γ for light vibrating parallellywith the directions of the a, b and c axis of the crystal differ fromeach other as seen in FIG. 3. For example, the values of Na, Nb and Ncof a single crystal of MOG belonging to the point group imm2 are Na =1.8428 Nb = 1.8432 and Nc = 1.897 when λ = 589.3.

As will be apparent from these values, a crystal belonging to the pointgroup imm2 shows birefringence which is the feature of an opticallybi-axial crystal.

A crystal plate of MOG having such a property is of a Z-plate, that is,cut at opposite surfaces perpendicularly with respect to the c axis. TheZ-plate of MOG designated by the reference numeral 3 is interposedbetween a polarized 1 and an analyzer 2 whose planes of polarizationcross at right angles with each other and whose plate surfaces areparallel to each other in such a manner that the direction of the c axisof the crystal plate 3 is perpendicular with respect to the planes ofpolarization as shown in FIG. 2. When a beam of white light enters thepolarizer 1 at right angles with respect to the latter, the white lightlinearly polarized by the polarizer 1 is turned into ellipsoidallypolarized light by the effect of double refraction of the crystal plate3, and the component of the ellipsoidally polarized light which isparallel to the polarizing direction of the analyzer 2 passes solelythrough the analyzer 2 so that interference colors can be observed dueto the phase difference between the various wavelengths which constitutethe white light. A crystal of such an irregular ferroelectric having thesymmetry of imm2 is cut into a plate whose sides are parallel to thecrystal axis, the faces of the plate are polished to be optically flatsurfaces, and electrodes are provided on the Z-planes thereof. When thecrystal is interposed in a diagonal position between crossed polars anda beam of white light is projected on the optical system, interferencecolors due to the birefringence appear depending on the thickness of thecrystal. This is attributable to the phase difference between the beamsof double refracted light passing through the crystal and having theplanes of polarization perpendicular with respect to each other, thatis, this phenomenon is caused by the retardation R. As is commonlyknown, the retardation R is related to the thickness d of the crystalthrough which the light beam is transmitted and the birefringence, i.e.,the difference .increment.n between the refractive indices concerning tothe transmitting light beam as follows: ##EQU1## The refractiveindicatrix of an irregular ferroelectric crystal relative to theprinciple elastic axis X, Y and Z is as shown in FIG. 3. Thus, a beam oflight advancing in the direction of the Z axis in FIG. 3 is refractedwith two different refractive indices α and β, and the birefringence Δnis given by the difference β - α. Similarly, a beam of light advancingin the direction of the X axis is refracted with two differentrefractive indices γ and α, while a beam of light advancing in thedirection of the Y axis is refracted with two different refractiveindices γ and β. In this respect, it is to be noted that the beam oflight advancing in the direction of the Z axis, that is, perpendicularlywith respect to the Z-planes of a Z-plate of MOG is most advantageouslyutilized so that the crystal plate of MOG can constitute a colormodulator because the lenght d of the path of light as well as thedifference β - α between the refractive indices α and β remainsinvariable even when the crystal plate of MOG is subject to thepolarization reversal. U.S. Pat. No. 3,586,415 referred to aboveutilizes this principle. The principle and structure of the apparatusdisclosed in said patent application will be described in detailhereunder.

When an electric field greater than the coersive field is applied to theZ-plate 3 of MOG shown in FIG. 2, the reversal of the spontaneouspolarization takes place and the plane of optic axis of the crystal isrotated by 90° with the result that the direction of rotation of theellipsoidally polarized light emerging from the crystal is reversed.Therefore, the retardation R in such a case has a sign opposite to thesign of the previous retardation R.

Referring to FIG. 4, a transparent and birefringent crystal 3₁ and aZ-plate of irregular ferroelectric crystal 3₂ (such as a Z-plate of MOG)are disposed in a polarizing apparatus comprising a polarizer 1 and ananalyzer 2 disposed in parallel with each other so that the Z-planes ofthe crystal 32 are perpendicular with respect to the optical axis of thepolarizing apparatus and the principal axis of these two crystals areoriented in the same direction. The retardations R₁ and R₂ by therespective crystals are added to each other when the crystal of MOG isnot subject to reversal of the polarization, but one of the retardationsis subtracted from the other when an electric field is applied to thecrystal of MOG to cause the polarization reversal in the latter crystalso that, in this latter case, the composite retardation by these twocrystals is represented by the difference between R₁ and R₂. Thus, theinterference colors due to the birefringence against white lightentering the polarizing apparatus in the case of the difference betweenR₁ + R₂ differ from those in the case of the relation R₂. According tosuch a method, an apparatus can be made in which an assembly comprisingthe combination of one or more birefringent crystal plates and at leastone Z-plate of irregular ferroelectric belonging to the point group imm2is interposed between a polarizer and an analyzer disposed in parallelwith each other and an electric field or a stress greater than thecoersive field or the coersive stress is applied to the irregularferroelectric crystal to reverse the spontaneous polarization of theirregular ferroelectric crystal thereby to modulate the hue or amount oflight transmitting through the above assembly before and after thereversal of the spontaneous polarization.

The inventors have discovered that certain substances belonging to thepoint groups i2-I and i2-II possess also the above property in additionto the crystals of irregular ferroelectrics belonging to the point groupimm2. Known irregular ferroelectric substances belonging to these pointgroups are tabulated in Table 1 as follows:

                  Table 1                                                         ______________________________________                                               Sub-                                                                          stance                                                                 Point                                                                         group           Name                                                          ______________________________________                                        imm2        KDP, MOG, boracite                                                i2-I                                                                                      Rochelle salt, ammonium cadmium                                   i2-II       sulfate, methyl ammonium                                                      aluminum sulfate 12-hydrate                                       ______________________________________                                    

In Table 1, point group imm2 which includes such species 42 mF mm2, 6m2F mm2 and 43 mF mm2 is more useful than other two groups.

According to the studies carried out by the inventors, those substanceshaving a crystal structure isomorphous with MOG and represented by theformula (R_(x) R'_(1-x))₂ 0₃.3Mo_(1-e) We 0₃ where R and R' represent atleast one of rare earth elements, x lies in the range of 0 to 1.0, and elies in the range of 0 to 0.2) have the property preferably usable inthe present invention. The substances represented by the above formulabelong crystallographically to the orthorhombic system Pba2 and belongto the point group mm2.

The substances represented by the formula (R_(x) R'_(1-x))₂ 0₃.3Mo_(1-e)We 0₃ having a crystal structure isomorphous with MOG preferablyemployed in the present invention will now be described. A method ofmaking a single crystal of (R_(x) R'_(1-x))₂ 0₃.3Mo_(1-e) We 0₃ (where Rand R' represent at least one of the rare earth elements, x lies in therange of 0 to 1.0, and e lies in the range of 0 to 0.2) is known fromthe disclosure of Japanese Patent Publication No. 3493/1968. However,the crystal structure isomorphous with MOG specified in this applicationis one in which the lattice parameters a and b are equal to each other.

The following is the result of measurement on MOG employed in thepresent invention by means of a 3-axis goniometer and X-ray diffractivemethod:

    a = 10.388 ± 0.005 A

    b = 10.426 ± 0.005 A

    c = 10.709 ± 0.005 A

thus, MOG is a crystal of the orthorhombic system and belongs to thepoint group mm2.

Eu₂ (Mo0₄)₃, Tb₂ (Mo0₄)₃, Dy₂ (Mo0₄)₃ and Sm₂ (Mo0₄)₃ are isomorphouswith MOG crystallographically and their lattice parameters measured bythe X-ray diffractive method are different from each other depending onthe a and b axis as shown in Table 2. All these compounds have the samecrystal structure as MOG.

                  Table 2                                                         ______________________________________                                        Sample   a(A° )                                                                             b(A° )                                                                              c(A° )                               ______________________________________                                        Eu.sub.2 (MoO.sub.4).sub.3                                                             10.377 ± 0.005                                                                         10.472 ± 0.005                                                                         10.655 ± 0.005                            Gd.sub.2 (MoO.sub.4).sub.3                                                             10.388 ± 0.005                                                                         10.426 ± 0.005                                                                         10.709 ± 0.005                            Dy.sub.2 (MoO.sub.4).sub.3                                                             10.331 ± 0.005                                                                         10.346 ± 0.005                                                                         10.603 ± 0.005                            Sm.sub.2 (MoO.sub.4).sub.3                                                             10.478 ± 0.005                                                                         10.511 ± 0.005                                                                         10.856 ± 0.005                            ______________________________________                                    

Single crystals of MOG, Sm₂ (Mo0₄)₃, Eu₂ (Mo0₄)₃, Tb₂ (Mo0₄)₃ and Dy₂(Mo0₄)₃ were cut in parallel with the {100}, {010} and {001} planesperpendicular with respect to the a, b and c axis, and an electric fieldor stress was applied to the crystal in order to produce a single domaintherein. We call this process for producing single domain "polling".(Whether the single domain is produced or not can be observed by placingthe single crystal beneath a polarization microscope, directingpolarized light in the direction of the c axis and suitably manipulatingthe crossed nicols.) A 3-axis goniometer was used to measure theintensity distribution of the light reflected from the respective planesof the single crystal. The {400}, {600}, {800}, {1000}, {003}, {004} and{005} planes were used for the reflection of light. Then, an electricfield of inverse polarity was applied to the single crystal in thedirection of the c axis to interchange the a and b axis, and therefracted light from the {040}, {060}, {080} and {0100} planes wasmeasured. In the measurement, a dispersing slit of 1°, a scattering slitof 1°, a light receiving slit of 0.1 mm and a Cu K.sub.α ray were used.The voltage and current applied to the X-ray source were 30 KV and 10mA, respectively. The scanning rate of the goniometer was 1/4 degree perminute and the Geiger counter has a radius of 185 mm. When the singlecrystal was then heated above the Curie temperature to release thepolarized state, any appreciable difference was not present between thelattice parameters a and b.

The component of a novel crystal structure employed in the elementaccording to the present invention is a single crystal of a chemicalcompound having a crystal structure of MOG and a solid solution of sucha chemical compound. However, such a crystal structure is dependent uponthe size of cations in the chemical compound. A different crystalstructure results when the size of the cations is too large or toosmall. The Arrhenius ionic radii of the rare earth ions, Sm⁺³, Eu⁺³,Gd⁺³, Tb⁺³ Dy⁺³ are 1.00 A, 0.98 A, 0.97 A, 0.93 A and 0.92 A,respectively. Therefore, (R_(x) R'_(1-x))₂ 0₃.3Mo_(1-e) We 0₃ (where Rand R' represent at least one of the rare earth elements, x lies in therange of 0 to 1.0, and e lies in the range of 0 to 0.2) including therare earth ions of such ion radii has a crystal structure isomorphous tothat of MOG.

The chemical compound having a crystal structure of MOG employed in thepresent invention is of the orthorhombic symmetry and belongs to thepoint group mm2. The spontaneous strain xs of the chemical compound isgiven by ##EQU2## and the chemical compound having such a unit cell andthe same crystallographic symmetry exhibits an especially marked effectfor polarization reversal. The properties of MOG employed in the presentinvention are enumerated as follows:

    ______________________________________                                        Color:    Colorless and transparent                                           Density:  4600 kg/m.sup.3                                                     Point group:                                                                            Orthorhombic, mm2 (ferroelectric phase)                                       at a temperature below the Curie point Tc,                                    Tetragonal, 42 m (paraelectric phase) at a                                    temperature above the Curie point Tc,                                         and belonging to the ferroelectric-ferro-                                     elastic species 42 mF mm2.                                          Phase transition                                                              temperature (Tc):                                                                           162° ± 3° C.                                   Melting point:                                                                              1170° C.                                                 Cleavage plane:                                                                             {110}, {001}                                                    Specific dielectric                                                           constant:     εc = 10.5, εa - εb = 9.5 (at                          20° C)                                                                 εa, εb and εc represent the                           specific dielectric constants in                                              the directions of the a, b and c                                              axis, respectively.                                             Spontaneous                                                                    ##STR1##                                                                     of the c axis)                                                                Spontaneous strain: 1.5 × 10.sup.-3                                     Modulus of                                                                     ##STR2##                                                                      ##STR3##                                                                      ##STR4##                                                                     Electrical resistance: Above 10.sup.10 Ω·cm                    Resistance to water                                                           and chemicals: Very strong                                                    Tendency to efflorescence                                                     and deliquescence: None                                                       ______________________________________                                    

A method of making MOG employed in the present invention will bedescribed hereunder.

EXAMPLE 1

Mixture of 361.8 grams of Gd₂ 0₃ and 431.7 grams of Mo0₃ is pressed intoa pellet type. The pellets of the said mixture are then placed in acrucible of platinum or in a crucible of alumina white being supportedon a plate of platinum, and are heated at 700° C. for 2 to 3 hours in anelectric furnace. After finishing this solid state reaction, the pelletsare taken out of the electric furnace, and ground into fine powder.Suitable quantity of the powder is pressed again into pellets. Thepellets are placed in a crucible and are heated at 1000° C. for 2 to 4hours in the electric furnace. The result of observation of the productby an X-ray diffractive method proved that the product had the crystalstructure of MOG.

Subsequently, MOG in powder form is placed in a platinum crucible and isheated to melt at about 1190° C. A seed crystal of 3 mm × 3 mm indiameter and 30 mm in length is fixed to the pulling-up shaft withplatinum ribbon is then soaked in the melt of MOG and the temperature isgradually reduced until the melt solidifies on the seed. In this case,the input to the induction coil in increased until the seed crystalattains a diameter of about 2 mm, during the pulling-up shaft is rotatedat a rate of 30 to 60 revolutions per minute. The input to the furnaceis then reduced until the crystal growing on the seed of 2 mm indiameter attains a diameter of about 10 to 20 mm. The pulling rate inthis case is 18 to 1.5 mm per hour as in the above case and the input isadjusted so that the diameter of the crystal lies in a fixed range of 10to 20 mm. When the length of the pulled-up crystal reaches a desiredvalue of 30 to 70 mm, the input to the furnace is increased again toreduce the diameter of the succeeding crystal portion in the melt andthe crystal is pulled up in somewhat rapidly and cut off the remainingcrystal portion in the melt. The crystal thus obtained is placed in anafterheater and the temperature is reduced at a rate of 50° to 100° C.per hour to prevent the cracks from developing in the crystal. A singlecrystal of MOG can be obtained by the above steps. The latticeparameters of single crystal of MOG thus obtained has measured afterpoling and obtained in the previously described values.

Crystallographic isomers having the crystal structure of MOG preferablyemployed in the present invention are enumerated in Table 3. Thecompounds ranging from Example 2 to Example 49 can be made by a methodof crystal growth analogous to the method described in Example 1, andthe reacting components in the amounts specified in the second column ofTable 3 are heated at a temperature below the melting point of eachcompound to form a solid solution. These compounds are then heated upand processed according to the steps described in Example 1, and singlecrystals are pulling up from the melt respectively.

                  Table 3                                                         ______________________________________                                                          Reacting components                                                           (mixing ratio)                                              Ex-                     Mo-                                                   am-  Chemical formula of                                                                              lyb-                                                  ple  single crystal     date   Rare earth oxide                               ______________________________________                                                                       (Sm.sub.2 O.sub.3)                             2    Sm.sub.2 (MoO.sub.4).sub.3                                                                       431.8                                                                                348.7                                                                         (Eu.sub.2 O.sub.3)                             3    Eu.sub.2 (MoO.sub.4).sub.3                                                                       431.8                                                                                352.0                                                                         (Dy.sub.2 O.sub.3)                             4    Dy.sub.2 (MoO.sub.4).sub.3                                                                       431.8                                                                                373.0                                                                         (Tb.sub.2 O.sub.3)                             5    Tb.sub.2 (MoO.sub.4).sub.3                                                                       833.6                                                                                748.8                                                                         (Gd.sub.2 O.sub.3)                                                                   (Sm.sub.2 O.sub.3)                      6    (Gd.sub.0.5 Sm.sub.0.5).sub.2 (MoO.sub.4).sub.3                                                  431.8                                                                                180.9  174.3                                                                  (Gd.sub.2 O.sub.3)                                                                   (Eu.sub.2 O.sub.3)                      7    (Gd.sub.0.5 Eu.sub.0.5).sub.2 (MoO.sub.4).sub.3                                                  431.8                                                                                180.9  176.0                                                                  (Gd.sub.2 O.sub.3)                                                                   (Tb.sub.2 O.sub.3)                      8    (Gd.sub.0.5 Tb.sub.0.5).sub.2 (MoO.sub.4).sub.3                                                  431.8                                                                                180.9  187.2                                                                  (Gd.sub.2 O.sub.3)                                                                   (Dy.sub.2 O.sub.3)                      9    (Gd.sub.0.5 Dy.sub.0.5).sub.2 (MoO.sub.4).sub.3                                                  431.8                                                                                180.9  186.5                                                                  (Gd.sub.2 O.sub.3)                                                                   (Yb.sub.2 O.sub.3)                      10   (Gd.sub.0.35 Yb.sub.0.65).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                343.7  19.7                                                                   (Gd.sub.2 O.sub.3)                                                                   (Ho.sub.2 O.sub.3)                      11   (Gd.sub.0.95 Ho.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                343.7  18.9                                                                   (Gd.sub.2 O.sub.3)                                                                   (Lu.sub.2 O.sub.3)                      12   (Gd.sub.0.95 Lu.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                343.7  19.9                                                                   (Gd.sub.2 O.sub.3)                                                                   (Tm.sub.2 O.sub.3)                      13   (Gd.sub.0.95 Tm.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                343.7  19.3                                                                   (Gd.sub.2 O.sub.3)                                                                   (Sc.sub.2 O.sub.3)                      14   (Gd.sub.0.95 Sc.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                343.7  6.9                                                                    (Gd.sub.2 O.sub.3)                                                                   (La.sub.2 O.sub.3)                      15   (Gd.sub.0.95 La.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                343.9  16.3                                                                   (Gd.sub.2 O.sub.3)                                                                   (Pr.sub.6 O.sub.11)                     16   (Gd.sub.0.95 Pr.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                343.9  17.0                                                                   (Gd.sub.2 O.sub.3)                                                                   (Y.sub.2 O.sub.3)                       17   (Gd.sub.0.6 Y.sub.0.4).sub.2 (MoO.sub.4).sub.3                                                   431.8                                                                                217.0  90.3                                                                   (Gd.sub.2 O.sub.3)                                                                   (La.sub.2 O.sub.3)                      18   (Gd.sub.0.6 La.sub.0.4).sub.2 (MoO.sub.4).sub.3                                                  431.8                                                                                217.0  130.8                                                                  (Gd.sub.2 O.sub.3)                                                                   (Dy.sub.2 O.sub.3)                                                     217.0  74.6                                    19   (Gd.sub.0.6 Tb.sub.0.2 Dy.sub.0.2).sub.2 (MoO.sub.4).sub.3                                       431.8                                                                                (Tb.sub.4 O.sub.7)                                                            78.8                                                                          (Gd.sub.2 O.sub.3)                                                                   (Eu.sub.2 O.sub.3)                                                     253.3  70.4                                    20   (Gd.sub.0.7 Eu.sub.0.2 Dy.sub.0.1).sub.2 (MoO.sub.4).sub.3                                       431.8                                                                                (Dy.sub.2 O.sub.3)                                                            37.3                                                                          (Gd.sub.2 O.sub.3)                                                                   (Sm.sub.2 O.sub.3)                                                     217.0  69.7                                    21   (Gd.sub.0.6 Sm.sub.0.2 Tb.sub.0.1).sub.2 (MoO.sub.4).sub.3                                       431.8                                                                                (Tb.sub.4 O.sub.7)                                                            39.4                                                                          (Gd.sub.2 O.sub.3)                                                                   (Eu.sub.2 O.sub.3)                                                     253.3  70.4                                    22   (Gd.sub.0.7 Eu.sub.0.2 Tb.sub.0.1).sub.2 (MoO.sub.4).sub.3                                       431.8                                                                                (Tb.sub.4 O.sub.7)                                                            39.4                                                                          (Gd.sub.2 O.sub.3)                                                                   (La.sub.2 O.sub.3)                                                     253.3  32.6                                    23   (Gd.sub.0.7 Y.sub.0.2 La.sub.0.1).sub.2 (MoO.sub.4).sub.3                                        431.8                                                                                (Y.sub.2 O.sub.3)                                                             45.2                                                                          (Gd.sub.2 O.sub.3)                                                                   (Eu.sub.2 O.sub.3)                                                     253.3  70.4                                    24   (Gd.sub.0.7 Eu.sub.0.2 Ho.sub.0.1).sub.2 (MoO.sub.4).sub.3                                       431.8                                                                                (Ho.sub.2 O.sub.3)                                                            37.8                                                                          (Gd.sub.2 O.sub.3)                                                                   (Sm.sub.2 O.sub.3)                                                     253.3  34.9                                    25   (Gd.sub.0.7 Sm.sub.0.1 Eu.sub.0.1 Y.sub.0.1).sub.2 (MoO.sub.4).sub.3                             431.8                                                                                (Eu.sub.2 O.sub.3 )                                                                  (Y.sub.2 O.sub.3)                                                      35.2   22.6                                                                   (Gd.sub.2 O.sub.3)                                                                   (Nd.sub.2 O.sub.3)                      26   (Gd.sub.0.95 Nd.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                343.7  16.8                                                                   (Gd.sub.2 O.sub.3)                                                                   (Tb.sub.4 O.sub.7)                                                     217.0  78.8                                    27   (Gd.sub.0.6 Tb.sub.0.2 Y.sub.0.1 La.sub.0.1).sub.2 (MoO.sub.4).sub.3                             431.8                                                                                (Y.sub.2 O.sub.3)                                                                    (La.sub.2 O.sub.3)                                                     22.6   32.6                                                                   (Gd.sub.2 O.sub.3)                                                                   (WO.sub.3)                              28   Gd.sub.2 (Mo.sub.0.95 W.sub.0.1 O.sub.4).sub.3 (MoO.sub.4).sub.3                                 431.8                                                                                280    70.0                                                                   (Sm.sub.2 O.sub.3)                                                                   (Eu.sub.2 O.sub.3)                      29   (Sm.sub.0.5 Eu.sub.0.5).sub.2 (MoO.sub.4).sub.3                                                  431.8                                                                                174.1  176.0                                                                  (Sm.sub.2 O.sub.3)                                                                   (Dy.sub.2 O.sub.3)                      30   (Sm.sub.0.5 Dy.sub.0.5).sub.2 (MoO.sub.4).sub.3                                                  431.8                                                                                174.1  186.5                                                                  (Sm.sub.2 O.sub.3)                                                                   (Tb.sub.4 O.sub.7)                      31   (Sm.sub.0.5 Tb.sub.0.5).sub. 2 (MoO.sub.4).sub.3                                                 431.8                                                                                174.1  187.5                                                                  (Sm.sub.2 O.sub.3)                                                                   (Yb.sub.2 O.sub.3)                      32   (Sm.sub.0.95 Yb.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                331.3  18.7                                                                   (Sm.sub.2 O.sub.3)                                                                   (Ho.sub.2 O.sub.3)                      33   (Sm.sub.0.95 Ho.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                331.3  18.9                                                                   (Sm.sub.2 O.sub.3)                                                                   (Lu.sub.2 O.sub.3)                      34   (Sm.sub.0.95 Lu.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                331.3  19.9                                                                   (Sm.sub.2 O.sub.3)                                                                   (Tm.sub.2 O.sub.3)                      35   (Sm.sub.0.95 Tm.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                331.3  19.3                                                                   (Sm.sub.2 O.sub.3)                                                                   (Sc.sub.2 O.sub.3)                      36   (Sm.sub.0.95 Sc.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                331.3  6.9                                                                    (Sm.sub.2 O.sub.3)                                                                   (Y.sub.2 O.sub.3)                       37   (Sm.sub.0.95 Y.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                 431.8                                                                                331.3  11.3                                                                   (Sm.sub.2 O.sub.3)                                                                   (Er.sub. 2 O.sub.3)                     38   (Sm.sub.0.9 Er.sub.0.1).sub.2 (MoO.sub.4).sub.3                                                  431.8                                                                                313.4  19.1                                                                   (Sm.sub.2 O.sub.3)                                                                   (Eu.sub.2 O.sub.3)                                                     209.4  105.4                                   39   (Sm.sub.0.6 Eu.sub.0.3 Er.sub.0.1).sub.2 (MoO.sub.4).sub.3                                       431.8                                                                                (Er.sub.2 O.sub.3)                                                            19.1                                                                          (Sm.sub.2 O.sub.3)                                                                   (Tb.sub.4 O.sub.7)                                                     244.0  78.8                                    40   (Sm.sub.0.7 Tb.sub.0.2 Y.sub.0.1).sub.2 (MoO.sub.4).sub.3                                        431.8                                                                                (Y.sub.2 O.sub.3)                                                             22.6                                                                          (Sm.sub.2 O.sub.3)                                                                   (Y.sub.2 O.sub.3)                                                      278.9  22.6                                    41   (Sm.sub.0.8 Er.sub.0.1 Y.sub.0.1).sub.2 MoO.sub.4).sub.3                                         431.8                                                                                (Er.sub.2 O.sub.3)                                                            19.1                                                                          (Sm.sub.2 O.sub.3)                                                                   (Dy.sub.2 O.sub.3)                                                     278.9  37.3                                    42   (Sm.sub.0.8 Dy.sub.0.1 Y.sub.0.05 Er.sub.0.05).sub.2 (MoO.sub.4).sub.         3                  431.8                                                                                (Y.sub.2 O.sub.3)                                                                    (Er.sub.2 O.sub.3)                                                     11.3   9.5                                                                    (WO.sub.3)                                                                           (Sm.sub.2 O.sub.3)                                                     70.0   174.1                                   43   (Sm.sub.0.5 Tb.sub.0.5).sub.2 (Mo.sub.0.9 W.sub.0.1).sub.3                                       388.6                                                                                (Tb.sub.4 O.sub.7)                                                            187.2                                                                         (Dy.sub.2 O.sub.3)                                                                   (La.sub.2 O.sub.3)                      44   (Dy.sub.0.95 La.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                369.3  16.3                                                                   (Dy.sub.2 O.sub.3)                                                                   (Pr.sub.6 O.sub.11)                     45   (Dy.sub.0.95 Pr.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                369.3  17.0                                                                   (Nd.sub.2 O.sub.3)                                                                   (Dy.sub.2 O.sub.3)                      46   (Dy.sub.0.95 Nd.sub.0.05).sub.2 (MoO.sub.4).sub.3                                                431.8                                                                                16.8   369.3                                                                  (Dy.sub.2 O.sub.3)                                                                   (Ho.sub.2 O.sub.3)                                                     298.4  37.8                                    47   (Dy.sub.0.8 Nd.sub.0.1 Ho.sub.0.1).sub.2 (MoO.sub.4).sub.3                                       431.8                                                                                (Nd.sub.2 O.sub.3)                                                            33.7                                                                          (Eu.sub.2 O.sub.3)                                                                   (Dy.sub.2 O.sub.3)                                                     211.2  74.6                                    48   (Eu.sub.0.6 Tb.sub.0.26 Dy.sub.0.2).sub.2 (MoO.sub.4).sub.3                                      431.8                                                                                (Tb.sub.4 O.sub.7)                                                            102.4                                                                         (Gd.sub.2 O.sub.3)                                                                   (Sm.sub.2 O.sub.3)                                                     217.0  34.9                                         (Gd.sub.0.6 Eu.sub.0.2 Sm.sub.0.1 Tb.sub.0.1 Dy.sub.0.1).sub.2                                          (Dy.sub.2 O.sub.3)                                                                   (Eu.sub.2 O.sub.3)                      49                      431.8                                                      (MoO.sub.4).sub.3         37.3   70.4                                                                   (Tb.sub.4 O.sub.7)                                                            39.4                                           ______________________________________                                    

According to the investigation performed by the inventors, a unit cellof an irregular ferroelectric crystal has bistable deformationsrelatively alternatable below the Curie temperature Tc at whichtemperature phase transition from the paraelectric phase to theferroelectric phase occurs. For example, a single crystal of MOG iscomposed of tetragonal lattices 4 in the paraelectric phase as shown inFIG. 5, but this tetragonal lattice 4 is deformable into four kinds oflattices 5₁, 5₁ ', 5₂ and 5₂ ' in the ferroelectric phase as shown inFIGS. 5a, 5b, 5c and 5d, respectively. These four kinds of lattices canbe classified into two sets of lattices, that is, a set of lattices 5₁and 5₁ ', and a set of lattices 5₂ and 5₂ ', which are relativelyswitchable by the polarization reversal. In each set of lattices,switching from one stable state to the other stable state occurs inresponse to application of an electric field of inverse polaritystronger than the coercive field. In this case, not only the switchingof the spontaneous strain but also a reversal of the spontaneouspolarization takes place, of course. Although these four kinds oflattices occur randomly in the crystal, the lattices of the samepolarization grow in the same domain as shown in FIGS. 6a and 6b inresponse to application of an external voltage or stress to the crystaland the lattices of one polarization and lattice state border thelattices of the other polarization and lattice state by a domain wall.With an increase in the external voltage, the lattices in the domain ofthe inverse polarity are affected by the external voltage and thepolarization is reversed together with the lattice deformation with theresult that the domain wall moves in a normal direction toward thedomain of opposite polarization. The domain wall which moves in responseto the application of voltage ceases its motion and is kept stationaryat the position when the application of the voltage is interrupted. Itis therefore possible to control the motion of the domain wall, that is,to cause forward and backward motion and to stop the motion of thedomain wall as desired by controlling the application of voltage orstress.

The possibility of occurrence between two sets of lattices of 5₁ or 5₁ 'and 5₂ or 5₂ ' is equal. In some cases, however, a domain pattern maypossibly appear in which the domains 5₁, 5₁ ' and 5₂, 5₂ ' cross atright angles with each other as shown in FIG. 6c and FIG. 7. Such adomain pattern is objectionable because any further growth of thedomains results in FIG. 7 that the domains impart a force to each otherat the boundary or at the cross-point therebetween until finally thecrystal itself would begin to separate.

In the single crystal of MOG, nuclei of domains (hereinafter to bereferred to merely as nuclei) emerge to form a single domain wallconfiguration and the nuclei have the tendency to grow in the directionnormal to the domain wall. When, for example, a D.C. voltage of about100 V is applied to a single crystal 3 of MOG 10 mm long, 10 mm wide and0.34 mm thick which is a Z-plate or cut in the direction parallel to the{001} plane for producing the nuclei in the single crystal, the domains5₁, 5₂, 5₁ ' and 5₂ ' grow in the direction perpendicular with respectto the <110> direction of the crystal plate 3 as shown in FIG. 7 and thenuclei impart a force to each other as they grow. Thus, the nucleicannot grow any further and an attempt to promote the growth by raisingthe voltage to a very high value tends to break the crystal plate 3.

Therefore, it is very important to secure the single wall motion. Thepresent invention eliminates the objectionable growth of the nucleicrossing at right angles with each other and to secure the single wallmotion.

Various preferred embodiments of the present invention will now bedescribed in detail with reference to the drawings.

EXAMPLE 1

a. A single crystal Z-plate 3 of MOG 10 mm long, 10 mm wide and 0.34 mmthick is cut in parallel with the {001} plane and the opposite surfacesof the crystal plate 3 are polished to optical flatness. The crystalplate 3 is heated up to about 500° C. and plated with transparentelectrodes. Tin chloride (Sn C14) is sprayed onto the opposite surfacesof the crystal plate 3 to provide a pair of transparent NESA electrodes6 thereon. b. The single crystal plate 3 of MOG is rendered to have amulti-domain configuration when the temperature is gradually decreasedto room temperature. c. The peripheral sides of the single crystal plate3 of multi-domain configuration obtained in this manner are cleaved by alaser knife utilizing the cleavage of the crystal so as thereby toremove the short-circuiting portions between the upper and lowertransparent electrodes 6. d. Then, as shown in FIG. 8a, a D.C. voltageof 100 V is applied across the upper and lower transparent electrodes 6disposed on the single crystal plate 3 of MOG thus obtained so as toproduce a single domain structure throughout the crystal plate 3. e.Subsequently, as shown in FIG. 8 and FIGS. 8a - 8e, parafin, wax, aplastic tape or painting-ink 7 of an electrically insulating naturehaving a sufficient resistance to an aqueous solution of salt is coatedon the transparent electrodes 6 with the exception of a portion 6aadjacent to one end edge of the upper electrode 6 along a direction of adomain wall, that is, along the <110> direction in the case of theZ-plate of MOG. Then, when the negative D.C.-voltage of 6 V is appliedto the upper transparent electrodes 6 and the positive electrode isdipped in an aqueous solution of salt, the exposed electrode portion 6ais gradually etched away as shown in FIG. 8b. The distribution ofdomains or polarities in the single crystal plate 3 of MOG treated inthe manner described above is determined by the polarities of theapplied voltage as shown in FIG. 8c. f. Then, the portion of theelectrode protecting film in the form of parafin, wax, plastic tape orpainting-ink covering a transparent electrode portion 6b at the endopposite to the portion 6a is removed and the upper electrode 6 isdipped in the aqueous solution of salt after the polarization reversalis performed only in an electroded portion by applying a voltage ofopposite polarity across the electrodes 6. As a result, the electrodeportion 6b is gradually etched away to provide an irregularferroelectric element adapted for single domainwall motion in which anucleus 3a of one polarization and a nucleus 3b of opposite polarizationare disposed on opposite sides of the Z-plate defined as seen in FIGS.8e and 8.

As will be apparent from the above description, the irregularferroelectric element for controllable single-domain is provided withthe nuclei of polarities opposite to each other on opposite sides of theperiphery of Z-plate. Thus, when a voltage is applied across theelectrodes, the nucleus of polarity equal to the polarity of the appliedvoltage grows gradually towards the opposite side of the crystal plateuntil it extends to the boundary of the nucleus of opposite polarityadjacent to the other end. When, conversely, a voltage of oppositepolarity is applied across the electrodes, the nucleus of polarity equalto the polarity of the applied voltage grows gradually and the domain ofopposite polarity to the applied voltage is gradually extinguished. Itis thus possible to freely control the growth and exhaustion of thedomains of polarities opposite to each other. The boundary or domainwall between the domains of opposite polarities is very clear-cut andflat plane and moves always along the <110> direction. Further, due tothe fact that such an irregular ferroelectric element includes alreadythe nuclei therein, application of a far smaller voltage can easilycause the domain all motion by the growing of the nucleus of onepolarity than when such a nucleus is newly grown in a Z-plate having nonucleus therein.

The irregular ferroelectric element for controllable single-domain ofthis structure has many advantages. First, the element can be securelyfixed to a support without adversely affecting the reversal ofpolarization because no reversal of polarization, hence no latticedeformation, occurs in the nucleus portion. Secondly, the positive andnegative domains grow depending on the polarity of applied voltage andtherefore the direction of domain growth is determined by the polarityof the applied voltage. It is thus possible to obtain a ferroelectricelement which is hardly cracked even when it is used for a high-speedcontinuous switching operation. Thirdly, the polarization reversal canbe initiated with a small applied voltage since the element includes thenuclei therein and requires no nucleation of reversed domain.

EXAMPLE 2

A Z-plate of 3 MOG single crystal 6 mm long, 2 mm wide and 2 mm thick issubject to steps similar to those described in Example 1 to produce apair of positive and negative domains at longitudinally opposite ends ofthe single crystal bar as shown in FIG. 9a. In this element, thereversal of the spontaneous polarization takes place easily in responseto application of pressure thereto. Portions 3a and 3b of an upperelectrode 6 are removed along the <110> direction of the single crystalplate 3 as shown in FIG. 9b.

EXAMPLE 3

A single crystal plate 3 of MOG is treated according to steps similar tothe steps (a), (b) and (c) described in Example 1, and a photo-resistfilm 7' is coated on each of transparent NESA electrodes 6 deposited onthe crystal plate 3 as shown in FIG. 19a. A mask 8 is then placed on theupper transparent electrode 6 as shown in FIG. 10b. After exposure, thenon-sensitized portions of the photo-resist film 7' are removed andalternate transparent electrode portions overlying the non-sensitizedphoto-resist film portions are removed by electrolysis while applying apositive voltage thereto. Then, the remaining transparent electrodeportions overlying the non-sensitized photo-resist film portions areremoved while applying a voltage of a sign opposite to the above voltageto obtain a ferroelectric element having such a domain configurationthat the nuclei of positive and negative polarization are alternatelyarranged as seen in FIG. 10c.

EXAMPLE 4

A Z-plate of a single crystal 3 of MOG 10 mm long, 10 mm wide and 0.34mm thick is cut at the sides thereof in parallel with the <110>direction. The portion adjacent to one end 3a of the single crystalplate 3 is securely fixed to a base plate 8 of material such as glass bya binder 9 such as an epoxy resin binder over a width of about 2 mm asshown in FIG. 11. Transparent electrodes 6 of SnO₂ are disposed on theZ-plates of the single crystal plate 3 and a voltage is applied acrossthe electrodes 6 so that the crystal plate 3 has a single domainconfiguration. Then, the portion adjacent to the opposite end 3b of thecrystal plate 3 is firmly secured to the glass plate 8 by the samebinder 9 over a width of about 2 mm.

While Examples 1, 2 and 4 have referred to an irregular ferroelectricelement in which nuclei for growing the domains of opposite polaritiesare produced at opposite ends of a crystal plate, an irregularferroelectric element in which a nucleus for growing a domain of onepolarity is disposed at one end only of a crystal plate can also bemade.

Some embodiments utilizing such a ferroelectric element for conrollablesingle-domain will be described hereunder.

EXAMPLE 5

As shown in FIG. 12a, a triangular shaped Z-plate 3 of MOG which is 10mm long at the two sides and 14 mm long at the base and has a thicknessof 0.34 mm is prepared. A method similar to that described in Example 1is employed to produce a nucleus of one polarity at an apex portion 3abetween the two sides in parallel with the <110> direction and a nucleusof opposite polarization at a base portion 3b also in parallel with the<110> direction. Four such crystal plates 3 are assembled so that theirapices 3a are in registration with each other at the same center 0 asshown in FIG. 12b. Transparent electrodes 6 of Sn0₂ are disposed on theZ-planes of the assembly and a D.C. power supply 10 at 150 V isconnected to the transparent electrodes 6 to constitute an electricallycontrolled shutter unit for transmitted light.

The electrically controlled shutter unit 3 is interposed together with aquarter-wave plate 3' between a polarizer 1 and an analyzer 2 as shownin FIG. 12c. The polarizer 1 and analyzer 2 are so arranged placed thattheir planes of polarization cross at right angles with each other(crossed polar) and are interposed in an optical path of a lens systemor any other optical system. When a voltage of a polarity the same asthe polarity of the nucleus 3a is applied to the electrically controlledshutter unit 3₁, the domain-wall of the nucleus 3a moves in thedirections of the arrows shown in FIG. 12b so that light beam can betransmitted through this portion. When, conversely, a voltage ofpolarity same as the polarity of the nucleus 3b is applied to theelectrically controlled shutter unit, the domain-wall moves in thedirections opposite to the arrows in FIG. 12b so that light transmissionis diminished and the total amount of light transmitted through thisportion is reduced. Thus, the element can be used as a sort of irisstop.

This shutter, when placed at the position of an iris stop in an opticalsystem, can serve as a perfect stop element for causing a uniform changeof the amount of light intensity throughout the entire surface of apicture.

EXAMPLE 6

A Z-plate 3 of MOG single crystal 10 mm long, 10 mm wide and 0.34 mmthick is cut at the four sides in the <110> direction, and a centralnucleus 3a and a pair of nuclei of opposite polarity are formed at thecenter and opposite ends, respectively, of the crystal plate 3 as shownin FIG. 13 according to a method similar to that described in Example 1.Transparent electrodes 6 of SnO₂ are deposited on the Z-planes of thecrystal plate 3 and a supply 10 of control voltage is connected to thetransparent electrodes 6 to constitute an optical slit element.

When a voltage of a polarity the same as the polarity of the nucleus 3ais applied across the transparent electrodes 6 from the power supply 10,the domain-walls (namely domain growth walls) W move in the directionsof the arrows, while when a voltage of polarity opposite to the polarityof the nucleus 3a is applied, the domain-walls W move in the directionsopposite to the arrows. Further, the direction of revolution ofpolarized light transmitted through the region of the nucleus 3a isopposite to the direction of revolution of polarized light transmittedthrough the remaining regions. Therefore, the combination of thisoptical slit element and a quarter-wave plate 3' usable in the visiblespectrum range may be interposed between a polarizer 1 and an analyzer 2having their planes of polarization crossed at right angles with respectto each other in a manner as shown in FIG. 12c thereby to obtain a sortof optical slit apparatus. In such an optical slit apparatus, thereoccurs no displacement of the center of the optical axis because thenucleus 3a grows and contracts equally in the transverse direction.Further, due to the fact that the nucleus 3a is in band form and thechange in the shape of the domain 3a takes place in the unit cells, theelement constitutes an optical slit of very high precision.

EXAMPLE 7

Two optical slit elements 3₁ and 3₂ of the kind described in Example 6are vertically disposed on the same optical axis in such a manner thattheir central nuclei cross at right angles with respect to each otherand their transparent NESA electrodes are connected in parallel with apower supply as shown in FIG. 14. When a voltage of a polarity the sameas the polarity of the central nuclei of the elements is applied acrossthe transparent electrodes, the domain-walls move in the directions ofthe arrows shown in FIG. 14, while when a voltage of polarity oppositeto the polarity of the central nuclei is applied, the domain-walls movein the directions opposite to the arrows. Thus, the direction ofrevolution of the plane of polarization for light transmitted throughthe nucleus regions of these two optical slit elements is opposite tothe direction of revolution of the plane of polarization for lighttransmitted through the remaining regions of the optical slit elements3₁ and 3₂. An electrically controlled shutter can be constituted bycombining these two optical slit elements 3₁ and 3₂ in series withquarter-wave plates and disposing the combination in a system includinga polarizer 1 and an analyzer 2 whose vibrational planes of polarizationare parallel to each other and a polarizer 3" whose vibrational plane ofpolarization crosses at right angles with the plane of polarization ofthe former as seen in FIG. 14.

EXAMPLE 8

Single crystal plates 3₁ and 3₂ of MOG which are Z-plates and cut at thefour sides in parallel with the <110> direction so as to serve asquarter-wave plates for visible light are provided with transparent NESAelectrodes 6 and are formed with nuclei I₁, II₁, I₂ and II₂ of polaritesopposite to each other at opposite ends according to a method similar tothat described in Example 1. The respective sets of the transparentelectrodes 6 on the electrically controlled shutter elements 3₁ and 3₂thus prepared are connected to power supplies 10₁ and 10₂, respectively.The elements 3₁ and 3₂ are arranged so that their Z-planes areperpendicular with respect to the optical axis and the nuclei I₁ and II₁of the element 3₁ are opposite to the nuclei II₂ and I₂ of the element3₂ as seen in FIG. 15. The combination of the elements 3₁ and 3₂ isinterposed between a polarizer 1 and an analyzer 2 so disposed thattheir planes of polarization cross at right angles with each other.Then, when control voltages are applied across the transparent NESAelectrodes 6 from the power supplies 10₁ and 10₂, the retardations oflight transmitted through the polarizer 1 and then through the elements3₁ and 3₂ are added to each other or substracted from each other as thedomain growth proceeds in the elements 3₁ and 3₂. Therefore, the lighttransmitted through the elements 3₁ and 3₂ and the analyzer 2 can beobserved as a motion of a bright portion through a dark portion on ascreen 11. It is to be noted that the voltages are applied to therespective sets of the transparent NESA electrodes 6 with a time delayof the kind as shown in FIG. 15a.

When the polarity of the applied voltage is reversed upon extension ofthe light-transmitting regions II₁ and II₂ of the elements 3₁ and 3₂ tothe boundary of the nucleus of the opposite polarity, the movingdirection of the light-transmitting domains is reversed so that thebright portion on the screen 11 moves in the reverse direction.

A bright spot moving substantially cyclically in one direction on thescreen 11 can be observed when the voltages applied to the elements 3₁and 3₂ have a difference in magnitude depending on the polarity thereofso that there is a difference between the rates of growth of eachlight-transmitting regions II₁, II₂ depending on the moving direction,that is, the rate of growth is slow in one direction but rapid in thereverse direction.

EXAMPLE 9

Referring to FIG. 16, the light transmitted through an apparatus asshown in FIG. 15 is focused by a lens 12 to be projected onto aplurality of photomultipliers 14 disposed behind a mask 13, and an inputsignal is supplied to a means 15 so that a voltage delivered from themeans 15 is applied to the transparent NESA electrodes 6 of theelectrically controlled shutter elements 3₁ and 3₂. A positive ornegative domain grows in the elements 3₁ and 3₂ in response to anexternal input signal, and an optical signal transmitted through thelight-transmitting regions of the elements 3₁ and 3₂ to reach the mask13 is converted into an electrical signal by the photomultipliers 14.This apparatus serves as a sort of optical pulse generator.

EXAMPLE 10

Referring to FIG. 17, a plurality of elements 3₁ I, 3₁ I', 3₁ I" and 3₁I'" and a plurality of elements 3₂ II, 3₂ II', 3₂ II" and 3₂ II'" of thekind shown in FIG. 15 are stacked up vertically in tiers to constitutetwo groups of shutter elements I and II. These elements are so arrangedthat the domain wall of the nucleus in the uppermost element extendsfirst toward the nucleus of the opposite polarity and then similargrowth of the nucleus in the successive elements is started. These twoshutter element group I and II are interposed between a polarizer 1 andan anaylzer 2 whose vibrational planes of polarization cross at rightangles with respect to each other. A screen 11 can be two-dimensionallyscanned with a flying spot when light is projected onto the apparatusand voltages are successively applied to the elements.

EXAMPLE 11

Referring to FIG. 18, elements 3₁, 3₂, 3₂ 40 and 3₁ 40 are similar tothose described in Example 9 but have a thickness of about 0.16 mm whichis half the thickness of the elements shown in FIG. 16 so that they actas 1/8-wave plates. These elements 3₁, 3₂, 3₂ 40 and 3₁ 40 areinterposed between a polarizer 1 and an analyzer 2 whose vibrationalplanes of polarization cross at right angles with each other, and theelements 3₂ ' and 3₁ ' are disposed in such a relation that they arerotated relative to the elements 3₁ and 3₂ through a certain angle of,for example, 90° in the planes perpendicular with respect to the lightbeam. Voltages of different periods from each other are applied to thetransparent NESA electrodes of the respective elements so that thetransmitted image of light L entering this apparatus can movetwo-dimensionally on a screen 11.

The electrically controlled shutter for transmitted light described inExample 8 can be utilized as a focal plane shutter for cameras so thatexposure at high speed can be carried out by varying the moving rate andwidth of the slit. Furhter, in the two-dimensional flying spot scannerdescribed in EXAMPLE 10 and 11, the horizontal and vertical scanningintervals of the flying spot can be controlled by the horizontal andvertical synchronizing pulses for a television. Therefore, as shown inFIG. 19, a real image of an object may be focused on a flying spotscreen 16 (the screen 11 in Examples 10 and 11) so that the output fromthe screen 16 can be converted into an electrical signal by means of aphotomultiplier device 15'. In another application as shown in FIG. 20,a beam of light from a light source 17 is passed through a flying spotscreen 16 and the light transmitted through a slide 18 is converted intoan electrical signal by means of a photomultiplier device 15'. In afurther application as shown in FIG. 20a, light passes through a flyingspot screen 16 is used to scan an object 18' and the light reflectedfrom the object 18' is sensed by a photomultiplier device 15' fordetection. In another application as shown in FIG. 21, the intensity ofa light beam from light source 17 is modulated by a picture signal 19and the modulated light is passed through a flying spot screen 16 forthe reproduction of the picture.

EXAMPLE 12

Referring to FIGS. 22a and 22b, a Z-plate 3 of MOG single crystal 20 mmlong, 15 mm wide and 0.33 mm thick is cut at the four sides in parallelwith the <110> direction and has its Z-planes polished to opticalflatness. Transparent electrodes 6 consisting essentially of SnO₂ aredeposited on the Z-planes at about 500° C., and then the opposite endedge portions 3a and 3b of the transparent NESA electrodes 6 are removedover a width of 1 mm by a method similar to that described in Example 1.A positive nucleus and a negative nucleus are formed in the crystalplate 3 at portions corresponding to the portions 3a and 3b,respectively, and the upper and lower electrodes 6 are connected to apower supply by lead-wires. The Z-plate 3 of MOG single crystal havingthe above thickness acts apparently as a quarter-wave plate over theentire visible spectrum range. The combination of the Z-plate 3 of MOGsingle crystal and a commercial quarter-wave plate 3' is interposedbetween a polarizer 1 and an analyzer 2 whose vibrational planes ofpolarization cross at right angles with each other as shown in FIG. 23.When a light-beam from a xenon lamp L is projected onto the apparatusand transmitted through the above plates to enter a slide projector 20,a picture can be obtained on a screen 11.

Application of a positive voltage to the element 3 causes gradual growthof the positive domain from the positive nucleus, and the retardationsare added to each other and subtracted from each other, respectively, inthe portions of light transmitted through the positive domain and thenegative domain and then through a quarter-wave plate 3'. Thus, theimage formed on the screen 11 can be partly erased.

The electrically controlled shutter may be disposed in place of the irisstop element in the optical system of a camera or slide projector so asto uniformly vary the amount of light over the entire area.

EXAMPLE 13

A Z-plate 3 of MOG single crystal is processed to the form shown inFIGS. 22a and 22b and is combined with five commercial half-wave plates3" as shown in FIG. 24. The combination is interposed between apolarizer 1 and an analyzer 2 whose vibrational planes of polarizationcross at right angles with each other. A light-beam emitted from a lightsource L is transmitted through the apparatus and a slide projector 21to form an image on a screen 11. The half-wave plates 3" are providedwith a pattern as shown in FIG. 24a. More precisely, the face portion iscut out in the first half-wave plate, the bottle portion is cut out inthe first and second half-wave plates, and the hair, eyes and otherportions are painted in black. Thus, the background of the picture isformed by the five half-wave plates, the face portion is formed by thefour half-wave plates, and the bottle portion is formed by the threehalf-wave plates.

The positive or negative domain grows in the crystal plate 3 of MOGdepending on the polarity of voltage applied thereto with the resultthat a change occurs in the color of light emitted from the source L ofwhite light and hence a change occurs in the hue of the face and bottleportions depending on the difference the retardations of lighttransmitted through the positive domain and light transmitted throughthe half-wave plates. When no voltage or stress is applied to thecrystal plate 3 of MOG, no change occurs in the polarization of thecrystal plate which is therefore maintained in the existing state.

While the embodiments described above have referred to the case in whicha set of polarizing elements, that is, a polarizer and an analyzer is sodisposed that the vibrational planes of polarization of these elementscross at right angles with each other, the present invention includesalso an arrangement in which the polarizing elements have theirvibrational planes of polarization crossed at any other suitable angle.

EXAMPLE 14

If electrodes are provided on the opposite Z-planes of a Z-plate of MOGcrystal which is 10 mm in the diameter and 2 mm in thickness and apressure of about 100 g is applied in the direction of b axis of thecrystal with the said electrode short-circuited, the spontaneous strainof the crystal is reversed.

If the electrodes are not short-circuited, the reversal of the strainwill not occur even under a pressure of 10 kg.

EXAMPLE 15

In the above Example 14, it is sometimes found that mutually orthogonaldomains are produced as indicated by A, B and A', B' in FIG. 25. If thepressure is further increased, the crystal is possible to break by aforce acting between the orthogonal domains.

To prevent this, the pressure may be applied in a direction slightly(1°C. - 30° ) inclined against the b axis in the Z-plane, or the samepurpose is attained by removing either one set of the A and A' domainsor the B and B' domains.

What is claimed is:
 1. An optical slit unit which employs an irregularferroelectric element comprising:a crystal Z-plate of irregularferroelectric material having a pair of opposing surfaces bounded by thesides of the plate, at least a pair of which sides opposing one anotherbeing cut in the <110> direction; and means, coupled to said pair ofopposing surfaces, for reversing the state of polarization of saidplate; and wherein said plate has a domain configuration such that saidplate includes a central nucleus-region of a prescribed polarity and twoside nucleus-regions having a polarity opposite that of said centralnucleus-region and being disposed on opposite sides of said centralnucleus-region, with a respective domain growth wall interposed betweensaid central nucleus-region and each of said side nucleus-regions.
 2. Anoptical slit unit according to claim 1, further comprising a pair ofpolarizing elements disposed in parallel, spaced apart in relation toeach other, and a quarter-wave plate, said Z-plate, said pair ofpolarizing elements and said quarter-wave plate being disposed opticallyin series, with said Z-plate and said quarter-wave plate being disposedbetween said polarizing elements.
 3. An optical slit unit according toclaim 1, wherein said Z-plate has two pairs of opposing sides defining arectangularly shaped plate, each side being cut in the <110> direction.4. An optical slit unit according to claim 3, wherein said meanscomprises a pair of transparent electrodes formed on said opposingsurfaces, and a voltage source electrically connected to saidtransparent electrodes.